JP2009019251A - Hydrogen storage alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy showing a high durability against repeated hydrogen absorption/desorption. <P>SOLUTION: The hydrogen storage alloy comprises 8-44 at.% Cr, 25-85 at.% V, 1-10 at.% Fe and the balance being unavoidable impurities and optionally contains ≤25 at.% Ti. Preferably, the alloy comprises 8-20 at.% Cr, 60-82 at.% V and 5-10 at.% Fe, and the content of the optional component Ti is preferably ≤5 at.%. The void volume per hydrogen atom in a unit crystal lattice is ≥4 Å<SP>3</SP>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hydrogen storage alloy, and more particularly to a hydrogen storage alloy having high durability against repeated hydrogen storage and release.

As a property of the hydrogen storage alloy, not only the hydrogen storage amount but also the durability against repeated storage and release of hydrogen is important. Various materials having high durability such as AB ₂ alloy and Laves phase alloy have been developed so far, but improvement of hydrogen storage capacity is demanded.

  Therefore, body-centered cubic (BCC) -based hydrogen storage alloys are attracting attention because they have a large void volume as a crystal structure and can be expected to have a high hydrogen storage capacity. However, it is necessary to improve durability for practical use. It was.

For example, Patent Document 1 discloses that the composition is TiaCrbFecVd where 20 ≦ a ≦ 45, 30 ≦ b ≦ 70, 0 ≦ c ≦ 15, and 5 ≦ d ≦ 45, the main phase is a BCC structure and includes a Laves phase. Storage alloys have been proposed. However, the void volume per hydrogen atom for the unit crystal lattice smaller and 3.7 Å ^3, liable to damage the generation of crystal lattice with repeated occlusion and release of hydrogen, there is a problem of low durability.

  Further, Patent Document 2 and Patent Document 3 disclose a hydrogen storage alloy having a BCC structure as a main phase in a Ti—Cr—Fe—V system, but it has not been improved from the viewpoint of durability.

JP 2004-169102 A JP 2004-27247 A JP 2003-96532 A

  An object of the present invention is to provide a hydrogen storage alloy having high durability against repeated hydrogen storage / release.

In order to achieve the above object, according to the present invention, the following composition:
Cr: 8 to 44 at%,
V: 25-85 at%,
Provided is a hydrogen storage alloy comprising Fe: 1 to 10 at%, and the balance: inevitable impurities.

  The hydrogen storage alloy of the present invention can have a BCC structure in which the crystal lattice is large and the unit crystal lattice has a large void volume per hydrogen atom by setting the composition within the specified range. Even if the release is repeated, the crystal lattice is hardly damaged and high durability can be exhibited.

  FIG. 1 shows the relationship between the amount of voids per hydrogen atom in a unit crystal lattice and the rate of deterioration (*) of the amount of occlusion due to repeated hydrogen occlusion / release.

(*: Degradation rate (%) = 100 × [Occlusion amount in the first cycle−Occlusion amount in the 40th cycle] / [Occlusion amount in the first cycle]. Details of the cycle test are as described in the examples.)
The composition of each alloy in the figure is as follows.

A (low pressure type BCC alloy): Ti ₂₅ -Cr ₅₀ -V ₂₅ (numbers are at%)
B (high pressure type BCC alloy): Ti ₂₅ —Cr ₅₀ —V ₂₀ —Mo ₅
C (high pressure type high VBCC _{alloy): Ti 11 -Cr 12 -V 71} -Mo 5 -Ni 1
D (invention BCC _{alloy): Ti 25 -Cr 44 -V 25} -Fe 6
E (TiCrMn _{alloy): Ti} 36 -Cr _{32 -Mn} 32
As clearly shown in the figure, the deterioration rate can be suppressed to 10% or less by setting the void amount to 4 ³ or more. The alloy composition of the present invention was limited to Cr: 8 to 44 at%, V: 25 to 85 at%, Fe: 1 to 10 at%, and the balance: inevitable impurities in order to make the deterioration rate 10% or less. Optionally, it can further contain up to 25 at% Ti. If even one of these component elements deviates from the above-mentioned limited range, a deterioration rate of 10% or less cannot be stably achieved.

  Desirably, Cr: 8 to 20 at%, V: 60 to 82 at%, and Fe: 5 to 10 at%. It is desirable that Ti as an optional component is 5 at% or less. By limiting to the desired range, the deterioration rate can be more stably reduced.

The alloy composition of the present invention is limited in consideration of the following. That is, if the crystal lattice is simply increased, the occlusion pressure becomes excessive and the occlusion does not occur, or significant cycle deterioration occurs due to excessive occlusion. Therefore, while considering the balance between the contents of Ti and V, which tend to expand the crystal lattice, and the contents of Cr, Fe, which tend to shrink the crystal lattice, each component element has a void amount of 4 以上³ or more. The content of was limited. In particular, the maximum hydrogen occlusion amount was adjusted with Fe, and a void amount of 4 ³ or more was secured while suppressing cycle deterioration due to excessive occlusion.

  Hydrogen storage alloys having various compositions shown in Table 1 were produced.

  The raw materials prepared in the above composition were melted at 1500 to 1600 ° C. in an inert gas (Ar) atmosphere and cast. Casting was performed by casting in a disk-shaped mold in an inert gas (Ar) atmosphere.

  The obtained cast sample was subjected to a homogenization heat treatment in which it was kept at about 1250 ° C. for 10 hours in an inert gas (Ar) atmosphere and then gradually cooled.

  The sample after the heat treatment was pulverized into granules having a particle size of about several mm to 0.1 mm and subjected to a cycle test.

  In the cycle test, 40 cycles of storing and releasing hydrogen at a pressure between 0.1 MPa and 33 MPa were performed at room temperature, and the ratio of the decrease in the hydrogen storage amount in the 40th cycle to the hydrogen storage amount in the first cycle was expressed as “deterioration”. Rate "(see formula (1) below).

Degradation rate (%) = 100 × [Occupation amount in the first cycle−Occlusion amount in the 40th cycle] / [Occlusion amount in the first cycle] (*: occlusion amount = effective hydrogen amount) (1)
Further, the void volume per hydrogen atom in the unit crystal lattice was calculated as “void / H” by the definition of the following formula (2).

Void / H (Å ³ ) = [lattice volume−constituent element occupation volume] / [maximum occlusion number of hydrogen atoms in one lattice] (2)
The measurement results of the deterioration rate and void / H are also shown in Table 1.

  Sample Nos. 1 to 5 are examples within the scope of the present invention, and sample Nos. 6 to 9 are comparative examples outside the scope of the present invention.

In Comparative Examples 6 to 9, which are outside the scope of the present invention, the void ratio / H is as small as less than 4 ³ , so the deterioration rate is as high as 21 to 26%. On the other hand, in Examples 1 to 5, which are within the scope of the present invention, the void ratio / H is as large as 4 ³ or more, so the deterioration rate is reduced to 6 to 11.

  According to the present invention, a hydrogen storage alloy having high durability against repeated hydrogen storage / release is provided.

The graph which shows the relationship between the amount of space | gap per hydrogen atom in a unit crystal lattice, and the deterioration rate of the occlusion amount by a hydrogen occlusion / release cycle about various hydrogen occlusion alloys.

Claims (5)

The following composition:
Cr: 8 to 44 at%,
V: 25-85 at%,
A hydrogen storage alloy comprising Fe: 1 to 10 at%, and the balance: inevitable impurities. In claim 1,
Cr: 8-20 at%,
V: 60-82 at%,
Fe: 5 to 10 at%
A hydrogen storage alloy characterized by   3. The hydrogen storage alloy according to claim 1, further comprising Ti: 25 at% or less.   The hydrogen storage alloy according to claim 3, wherein Ti: 5 at% or less. The hydrogen storage alloy according to any one of claims 1 to 4, wherein the unit crystal lattice has a void volume per hydrogen atom of 4 ³ or more.

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